In order to investigate the tonal noise generated by viscous blade/vane interaction in a typical transonic bypass engine fan stage, time domain calculations were carried out with the non-linear Navier-Stokes solver TRACE. The propagating acoustic field was obtained by a modal decomposition of near field flow data. Comparisons with available experimental data in the bypass duct casing are presented. Different OGV designs of the investigated fanstage were evaluated with respect to the emitted tonal noise of the stage. To ensure the correct modal structure of the acoustic field it is vital to employ the correct blade count ratio in numerical simulations. To accomplish this efficiently, phase-lagged boundary conditions were incorporated into the employed flow solver. The method has been validated using a counter-rotating propfan configuration and was then applied for the three dimensional, spatially highly resolved fanstage calculation.

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